1. Field of the Invention
The present invention relates to a method for tracking defective functions in the operation of heater plugs in a diesel engine of a vehicle, provided with a control unit for the control of its heater plugs—the preheater control unit—by the steps of                monitoring at least one operating parameter of the heater plugs and/or of the preheater control unit;        generating a fault message when the operating parameter so monitored devates from a predefined nominal value or nominal state of the operating parameter;        and storing the fault message.        
2. Description of Related Art
From MTZ Motortechnische Zeitschrift 61 (2010), pp. 668 to 675, “Das elektronisch gesteuerte Gühsystem ISS für Dieselmotoren (The electronically controlled ISS preheater system for diesel engines)”, there has been known a control unit for heater plugs of a diesel engine, hereinafter referred to as preheater control unit, the essential components of which consist of a microprocessor for the control of all functions, a plurality of MOSFET power semiconductors for switching the different heater plugs on and off, an electric interface for communication with the engine control and an internal power supply for the microprocessor and the interface. The microprocessor controls the power semiconductors, reads their state information and communicates with the engine control via the electric interface. The interface serves the function to condition the signals required for communication between the engine control and the microprocessor. The preheater control unit preferably is mounted directly on the engine.
The heater plugs within the ISS preheater system are individually driven by the power semiconductors. This allows selective diagnosis and protective functions to be realized. An overcurrent detection unit interrupts the respective preheat circuit when excessive load currents are encountered, for example due to a short-circuit. When the power semiconductors assume an inadmissibly high temperature, due to self-heating or excessively high environmental temperature, the circuit is interrupted whereby destruction of the power semiconductor is prevented. An open load circuit can be detected as well. All that state information can be transmitted to the engine control, just as the electric power consumed by the preheater system.
Any faults encountered can be reported, once detected, to the engine control unit by the ISS preheater system and can be stored in a fault memory of the engine control unit. In addition, the preheater control unit comprises a fault memory that counts the number of times a fault occurs.
The entries in the fault memory of the engine control unit can be read out using a diagnosis computer that is connected to a diagnosis interface of the vehicle in a workshop. The fault memory of the preheater control unit can be read out either via the same interface or by directly contacting the preheater control unit via a special tool. The faults indicated are to provide the workshop personnel with information as to whether and where the preheater control unit may need to be repaired or to be exchanged or if any heater plugs should be exchanged. Further, it is the intention to assist subsequent analysis carried out by the supplier of the motor vehicle and/or by the supplier of the preheater control unit.